water pressure no staying after pump shuts off

I have a digital pressure switch. It is set at 34 and 68. The pump kicks on at the correct point 33 but it jumps to 70 right away and then runs for a second and shuts off. The pressure switch shows 40. Why does the pressure show 72 when it shuts off and then drops to 40 when it shuts off? Nothing is running in the house when this occurs.

water pressure no staying after pump shuts off

water pressure no staying after pump shuts off

Your expansion tank or pressure tank may be saturated. If the air pocket in the tank is too small, then the pump will sense a sudden pressure rise and then shut off. Then any slop in the back flow preventer causes the pressure to drop back a bit. If the pressure does not fall back too far then the pump won't come back on immediately and repeat the off and on, pressure rise and drop regimen over and over.

If you turn off the pump, empty all the water out of the pressure tank, expand the bladder all the way down to the water inlet end (maximizing the air pocket), let out the excess air under pressure, and then put everything back together and turn the pump back on, you will usually get the system back in order with only small pressure changes close to the correct pressure (or only occasional small deviations outside the high and low pressure limits you set). Your pump or pressure tank may have more precise instructions for setting the correct pressure.

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